Name a primary preventive measure against HIV transmission.

The use of condoms is a primary preventive measure against HIV transmission because they provide a physical barrier that reduces the risk of the virus being passed between sexual partners. Condoms can effectively block the exchange of bodily fluids, which is the primary route of HIV transmission during sexual activity. When used consistently and correctly, they are highly effective in preventing not only HIV but also other sexually transmitted infections (STIs).

Regular blood testing is important for monitoring HIV status and the effectiveness of treatment but does not prevent transmission. Avoiding sharing food is not relevant to HIV transmission, as the virus is not spread through casual contact like sharing meals. Annual vaccinations can prevent certain viral infections but currently do not include a vaccine for HIV, making them ineffective as a preventive measure against this specific virus.